1. Field of the Invention
The present invention generally relates to a liquid crystal display apparatus, and more particularly to a liquid crystal display apparatus having a front light optical waveguide.
2. Description of the Related Art
Owing to recent advances in the reduction of size and power consumption of computer apparatuses, more computer apparatuses are able to be used outdoors. A liquid crystal display apparatus, serving as an indispensable display apparatus for mobile purposes, is required to be visible in bright environments such as the outdoors, and further is desired to provide energy saving benefits. Under this situation, a reflective type display element is gaining attention. In addition to the growing demand in size reduction of related apparatuses, there is also a demand in obtaining thinner liquid crystal display apparatuses.
Although a reflective type liquid crystal display apparatus is provided in answer to such demands, the reflective type liquid crystal display apparatus has a disadvantage, for example, of being unable to be viewed under dark environments. For overcoming this disadvantage, a reflective type module, which is mounted with a front light serving as its lighting unit, is provided. The module, however, has a thickness that is yet to be reduced.
As a known conventional art, transmissive liquid crystal display apparatuses using a backlight are shown in, for example, Japanese Patent Laid-Open Application Nos. 8-146224 or 2002-279812. FIG. 1 is a representative cross-sectional view of a backlight type transmissive or semi-transmissive liquid crystal display apparatus. The liquid crystal display apparatus mainly includes, for example, a liquid crystal panel 1, a driver IC package 3, a printed circuit board 4, a linear light source 5, an optical waveguide 7, and a metal casing (first metal casing) 9.
The liquid crystal panel 1 has two transparent substrates 1a, 1b serving to hold a liquid crystal, and two polarization elements 1c, 1d. The driver IC package 3 has a flexible substrate 3b on which a driver IC 3a for driving the liquid crystal panel 1 is mounted. The printed circuit board 4 has a short-sized electronic component (hereinafter referred to as “short component 4a”) and a tall-sized electronic component (hereinafter referred to as “tall component 4b”). One end of the driver IC package 3 is connected to the liquid crystal panel 1, and the other end is connected to the printed circuit board 4.
A cold-cathode fluorescent tube is mainly employed as the linear light source 5. The linear light source 5 is disposed at a side portion of the optical waveguide 7, so that the light of the linear light source 5, incoming from a side of the optical waveguide 7, is incident upon the optical waveguide 7. A reflective board 6 is situated at the outer periphery of the linear light source 5 for suitably guiding light to the optical waveguide 7.
The optical waveguide 7 has a cuneatic shape, and is formed from a transparent acrylic board material. As the incident light incoming from the side of the optical waveguide 7 is repetitively reflected inside the optical waveguide 7, the entire plane facing the liquid crystal panel 1 is illuminated. An optical sheet 8 is disposed on an optical light emitting plane of the optical waveguide 7 for adjusting the direction of the light emitted from the optical waveguide 7. Furthermore, the metal casing 9 has an opening that is substantially the same shape as the display area of the liquid crystal panel 1.
The backlight type transmissive or semi-transmissive liquid crystal display apparatus provides a thin sized structure by disposing the printed circuit board 4 toward the thinner side (left side in the drawing) of the cuneatic optical waveguide 7 and disposing the tall component 4b of the printed circuit board 4 toward the thinnest part of the cuneatic optical waveguide 7. However, the backlight type transmissive or semi-transmissive liquid crystal display apparatus under bright environments, such as the outdoors, is unable to provide a satisfactory visibility since solar light or the like cancels the backlight originating from the linear light source 5 and the optical waveguide 7.
FIG. 2 is a cross-sectional view of a front light type liquid crystal display apparatus that is proposed for solving such problem. In FIG. 2, like components are denoted by like numerals as of FIG. 1 and will not be further described. It is to be noted that numeral 2 indicates a polarization element.
In the front-light type liquid crystal display apparatus, the position between the liquid crystal panel 1 and the optical waveguide 7 is flipped (reversed) for allowing the optical waveguide 7 to illuminate a display portion of the liquid crystal panel 1 from the front. Furthermore, with the front-light type liquid crystal display apparatus, the optical waveguide 7 is shaped as a cuboid.
Although the front-light type liquid crystal display apparatus is able to solve the aforementioned visibility problem, it raises a problem of increasing the thickness of the liquid crystal display apparatus owing to the cuboid shape of the optical waveguide 7. More specifically, since the printed circuit board 4 is disposed on the backside of the liquid crystal panel 1 by bending of the driver IC package 3, the thickness H1 of the side (left side in FIG. 2) where the printed circuit board 7 is situated becomes larger than the thickness H2 of the side (right side in FIG. 2) opposite to the side where the printer circuit board 7 is situated.
FIG. 3 shows another front-light type liquid crystal display apparatus which uses a cuneatic optical waveguide 7. However, as shown in the drawing, an unnecessary space is created between the liquid crystal panel 1 and the optical waveguide 7, thereby precluding reduction of the thickness of the liquid crystal display apparatus. Therefore, although this front-light type liquid crystal display apparatus provides a sufficient visibility in bright environments such as the outdoors, the problem of being unable to reduce thickness remains unsolved.